1. Field of the Invention
The present invention relates to an IC socket, and more specifically an IC socket for testing a grid array package.
2. Description of Related Art
In general, an IC socket comprising a resin body and a plurality of metallic contacts each including a connecting terminal for electrically connecting to a corresponding lead or bump of a semiconductor package and a lead formed integrally with the connecting terminal and adapted to be inserted into a corresponding through-hole of a printed circuit board. FIGS. 9A and 9B are diagrammatic sectional views illustrating the structure of conventional IC sockets. As shown in these drawings, an IC socket is assembled by forcibly inserting a contact 1 into a contact fixing hole 3 of an IC socket body 2.
Recently, a variety of semiconductor packages have appeared, and in order to minimize the size of the semiconductor packages, the package is gradually shifting from a quad flat package (QFP) comprising a number of leads 13 outward extending from a periphery of a package body 12 as shown in FIG. 10, to a grid array package such as a ball grid array (BGA) package 14 having a number of solder bumps 15 formed in the form of a matrix on a lower surface of the package to constitute electric contacts of the package, as shown in FIGS. 11A and 11B, a pin grid array (PGA) package, and a land grid array (LGA) package, since these grid array packages can be used at a relatively low cost in place of QFP.
An IC socket used for testing an electric characteristics of the grid array packages such as BGA, PGA and LGA packages, has contacts of a spring structure so that the contacts are brought into pressure-contact with the electric contacts of the package such as leads or solder bumps. Because the contacts of the IC socket are pressure-contacted with the lead or solder bumps of the package, there occurs a phenomenon that a material of the electric contacts of the package is transferred to the contacts of the IC socket, with the result that an electrical contacting condition becomes poor, and therefore, it becomes necessary to frequently exchange the IC socket.
In the prior art, it was a general practice to fix an IC socket 2 to a test board 6, as shown in FIG. 12, by inserting contact pins id extending from the IC socket body 2, into through-holes 6a of the test board 6 from one surface of the test board 6, and then by soldering a tip end portion of the contact pins 1d projected from the other surface of the test board 6, by a solder 19. However, since it is difficult to exchange the IC socket under this practice, it has been proposed to make the IC socket detachable, as shown in FIG. 13, by providing an adapter socket 7 having a corresponding number of pin sockets 8, by soldering the pin sockets 8 to the test board 6 by a solder 19, and on the other hand, by inserting the contact pins 1d of the IC socket body 2 in the pin sockets 8 so that the contact pin 1d is grasped by a contact spring 8a in the inside of the pin socket 8.
However, in the IC socket shown in FIG. 13, if a fixing and grasping force for the contact 1 in the IC socket is inferior to an insertion pressure of the contact pin 1d into the pin socket 8 applied when the IC socket body 2 is fixed to the adapter socket 7, the contact pins are often deviated from each other, and in an extreme case, the contact falls away from the IC socket body. FIG. 14 is a diagrammatic enlarged partial view of the contact 1 and the IC socket body 2. When the contact 1 is inserted in and fixed to the contact fixing hole 3 of the IC socket body 2, the fixing and grasping force F.sub.0 acts on the contact 1 from the contact fixing hole 3, and the insertion pressure F.sub.1 acts on the contact 1 from a lower position, as shown in FIG. 15. When the relation between these forces becomes F.sub.0 &lt;F.sub.1, the contact 1 falls out from the IC socket 2, as designated by Reference Numeral 20 in FIG. 16.
In order to prevent the falling-out of the contact, Japanese Patent Application Pre-examination Publication No. JP-A-07-058250 discloses a technology in which, as shown in FIG. 2 of JP-A-07-058250, a barb 10b is formed on each of opposite side surfaces of a contact pin 10, so that when the contact pin 10 is inserted into a through hole of an IC socket body 9, the contact pin 10 is prevented from falling out from the IC socket body 9 by action of a wedge effect of the barb 10b. In this proposal, however, it is impossible to exchange the contact.
There has been also disclosed an IC socket for a plat package such as the QFP having a number of connection leads extending outward from the periphery of the package, the IC socket being configured to firmly hold the contacts by a hold-down plate, as another means for preventing the contact from falling out from the IC socket body.
For example, Japanese Utility Model Application Pre-examination
Publication No. JP-A-07U025594 discloses an IC socket including an upper plate member and a lower plate member and having a structure in which, as shown in FIG. 3 of JP-A-07U025594, a fixing contact 31 in the form of a wedge having a lead 32 to be inserted into a through hole of a printed board 61 is driven into the lower plate member 11, and on the other hand, the upper plate member 21 is provided with a movable contact 35 which can be moved dependently upon the kind of the IC package.
In this IC socket, however, the fixing of the movable contact 35 by the upper plate member 21 is achieved by depressing opposite ends of a stationary contact portion 36 of the movable contact 35 by means of the upper plate member 21. Therefore, the size of the movable contact becomes large, with the result that this IC socket cannot be applied to an IC socket for the grid array package such as BGA package. Japanese Utility Model Application Post-examination Publication No. JP-B-04U000553 discloses an IC socket having, as shown in FIG. 2 of JP-B-04U000553, a number of turned contact pins 5 arranged and aligned on a base plate 1 and a hold-down plate 7 put on a base portion of the turned contact pins 5, the hold-down plate 7 being depressed by a body member 3, so that the contact pins 5 are fixed by the body member 3 through the intermediary of hold-down plate 7. However, this IC socket can be applied for only the flat packet, and cannot be applied to a high density package such as the grid array package having a number of contacts arranged on a bottom surface of the package.